[PATCH 0/16] Pid namespaces

sukadev at us.ibm.com sukadev at us.ibm.com
Mon Jul 9 21:26:19 PDT 2007

I am not able to find a specific patch that this might be in,
but what happens when the child-reaper of a container exits ?
Do you terminate all processes in the container ? I thought
that was discussed earlier and the consensus was to terminate
all processes in that container and its subordinate containers.

Is that not the case now ?


Pavel Emelianov [xemul at openvz.org] wrote:
| This is "submition for inclusion" of hierarchical, not kconfig
| configurable, zero overheaded ;) pid namespaces.
| The overall idea is the following:
| The namespace are organized as a tree - once a task is cloned
| with CLONE_NEWPIDS (yes, I've also switched to it :) the new
| namespace becomes the parent's child and tasks living in the
| parent namespace see the tasks from the new one. The numerical
| ids are used on the kernel-user boundary, i.e. when we export
| pid to user we show the id, that should be used to address the
| task in question from the namespace we're exporting this id to.
| The main difference from Suka's patches are the following:
| 0. Suka's patches change the kernel/pid.c code too heavy.
|    This set keeps the kernel code look like it was without
|    the patches. However, this is a minor issue. The major is:
| 1. Suka's approach is to remove the notion of the task's 
|    numerical pid from the kernel at all. The numbers are 
|    used on the kernel-user boundary or within the kernel but
|    with the namespace this nr belongs to. This results in 
|    massive changes of struct's members fro int pid to struct
|    pid *pid, task->pid becomes the virtual id and so on and
|    so forth.
|    My approach is to keep the good old logic in the kernel. 
|    The task->pid is a global and unique pid, find_pid() finds
|    the pid by its global id and so on. The virtual ids appear
|    on the user-kernel boundary only. Thus drivers and other 
|    kernel code may still be unaware of pids unless they do not
|    communicate with the userspace and get/put numerical pids.
| And some more minor differences:
| 2. Suka's patches have the limit of pid namespace nesting. 
|    My patches do not.
| 3. Suka assumes that pid namespace can live without proc mount
|    and tries to make the code work with pid_ns->proc_mnt change
|    from NULL to not-NULL from times to times.
|    My code calls the kern_mount() at the namespace creation and
|    thus the pid_namespace always works with proc.
| There are some small issues that I can describe if someone is
| interested.
| The tests like nptl perf, unixbench spawn, getpid and others
| didn't reveal any performance degradation in init_namespace
| with the RHEL5 kernel .config file. I admit, that different
| .config-s may show that patches hurt the performance, but the
| intention was *not* to make the kernel work worse with popular
| distributions.
| This set has some ways to move forward, but this is some kind
| of a core, that do not change the init_pid_namespace behavior
| (checked with LTP tests) and may require some hacking to do 
| with the namespaces only.
| Patches apply to 2.6.22-rc6-mm1.

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